1. Field of the Invention
The present invention relates to a developing device, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
In an electrophotographic apparatus such as a copier, a printer, and a receiver of a facsimile, a rotating image carrying member is uniformly charged by a charging member, and laser light is applied to the charged image carrying member, whereby an electrostatic latent image is formed. Then, toner is supplied to the electrostatic latent image by a developing device, whereby the electrostatic latent image is developed into a toner image. Subsequently, the toner image is transferred from the image carrying member to a transfer material (a recording material), and the toner image on the transfer material is fixed by heating or the like. Thus, the transfer material has an image. Meanwhile, the static electricity on the surface of the image carrying member that has undergone the transfer of the toner image is eliminated, and residual toner is removed from the surface of the image carrying member. Thus, the electrophotographic apparatus is ready for forming another image.
The developing device includes a developing chamber and a toner container that contains toner. The developing chamber is provided with a developing roller, a toner supplying member that supplies toner to the surface of the developing roller, and so forth. The developing chamber is further provided with a toner regulating member that regulates the toner supplied to the surface of the developing roller by the toner supplying member into a thin layer having a more uniform thickness. With the rotation of the developing roller, the thin layer of toner is conveyed to the outside of the developing device. The thin layer of toner then adheres to the electrostatic latent image on the rotating image carrying member that is provided against a portion of the developing roller that is exposed to the outside of the developing device, whereby the electrostatic latent image is visualized. Thus, a toner image is formed on the image carrying member.
Before the developing device starts to be used, toner remains contained in the toner container. When the developing device starts to be used, the toner starts to be fed into the developing chamber. Hence, before the developing device starts to be used, the developing roller is directly in contact with the toner regulating member and the toner supplying member.
Japanese Patent Laid-Open No. 8-227212 addresses problems such as damage to a toner supplying member attributed to the direct contact between a developing sleeve and the toner supplying member in a developing device that is yet to be used. According to Japanese Patent Laid-Open No. 8-227212, such a problem is solved by employing a toner supplying member having cells on its outermost layer and by providing powder having specific chargeability at least on the surface of the toner supplying member.
According to Japanese Patent Laid-Open No. 2007-33538, the above problem is solved by providing powder whose glass transition temperature is 80° C. or higher at least on the surface of a toner supplying member.
However, according to a review of the developing device disclosed by Japanese Patent Laid-Open No. 2007-33538 that has been conducted by the present inventors, if the developing device that is yet to be used is vibrated or something during transportation, resulting electrophotographic images may have nonuniformity in the form of stripes in a portion thereof corresponding to a portion of the surface of the developing roller that is in contact with the toner regulating member. Hereinafter, the nonuniformity in the form of stripes that may appear in an electrophotographic image is also referred to as “banding.” The banding tends to be particularly pronounced in a halftone image. This is probably because of some change that occurs in the portion of the surface of the developing roller that is in contact with the toner regulating member.
Such a change in the surface of the developing roller that affects the quality of resulting electrophotographic images is occasionally referred to as “electrostatic memory.” A phenomenon of the appearance of such an “electrostatic memory” is occasionally referred to as “generation of an electrostatic memory.”
Accordingly, the present invention is directed to providing a developing device in which an electrostatic memory that may cause banding in electrophotographic images does not tend to be generated on a developing roller even if the developing device that is yet to be used is vibrated during long-time transportation.
The present invention is also directed to providing an electrophotographic apparatus that is capable of stably outputting high-quality electrophotographic images.